A guard ring region may be formed in a semiconductor device such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) to surround a region at which a semiconductor element is provided in order to suppress a semiconductor element from being broken by concentration of an electric field.
For example, Japanese Patent Laying-Open No. 2008-4643 (Patent Document 1) describes a structure of a MOSFET made of silicon, the MOSFET including an element region and a termination region formed to surround the element region, a guard ring being formed at the termination region. According to the MOSFET described in Japanese Patent Laying-Open No. 2008-4643, a guard ring layer and an embedded guard ring layer are formed to have curvatures at a corner portion of the outermost base region such that they are concentric to each other. Moreover, in order to suppress the concentration of electric field at the corner portion of the outermost base region, the outermost base region is configured to have a radius of curvature about twice to four times as large as the thickness of the drift layer.